Effects of extracellular nucleotides and their hydrolysis products on volume regulatory decrease of hepatocytes from trout (Oncorhynchus mykiss).

DIEGO E, PAFUNDO; MUT, PAULA; PERÉZ RECALDE, MERCEDES; RODOLFO MARTIN GONZALEZ LEBRERO; FACHINO, VICTORIA; KRUMSCHNABEL, G; PABLO JOSÉ, SCHWARZBAUM

AMERICAN JOURNAL OF PHYSIOLOGY-REGULATORY, INTEGRATIVE AND COMPARATIVE PHYSIOLOGY

AMER PHYSIOLOGICAL SOC

Año: 2004 vol. 287 p. 1 - 1

0363-6119

In trout hepatocytes, hypotonicswelling is followed by a compensatory shrinkage called regulatoryvolume decrease (RVD). It has been postulated that extracellular ATPand other nucleotides may interact with type 2 receptors (P2) tomodulate this response. In addition, specific ectoenzymes hydrolyzeATP sequentially down to adenosine, which may bind to type 1receptors (P1) and also influence RVD. Accordingly, in this study, weassessed the role of extracellular nucleoside 5Ј-tri- and diphosphatesand of adenosine on RVD of trout hepatocytes. The extent of RVDafter 40 min of maximum swelling was denoted as RVD40, whereasthe initial rate of RVD was called vRVD. In the presence of hypotonicmedium (60% of isotonic), hepatocytes swelled 1.6 times followed byvRVD of 1.7 minϪ1 and RVD40 of 60.2%. ATP, UTP, UDP, or ATP␥S(P2 agonists; 5 ␮M) increased vRVD 1.5?2 times, whereas no changeswere observed in the values of RVD40. Addition of 100 ␮M suraminor cibacron blue (P2 antagonists) to the hypotonic medium producedno effect on vRVD but a 53?58% inhibition of RVD40. Incubation ofhepatocytes in the presence of either 5 ␮M [␥-32P]ATP or[␣-32P]ATP induced the extracellular release of [␥-32P]Pi (0.21nmol 1⁄7 10Ϫ6 cellsϪ1 1⁄7 minϪ1) and [␣-32P]Pi (ϳ8 ϫ 10Ϫ3 nmol 1⁄7 10Ϫ6cellsϪ1 1⁄7 minϪ1), suggesting the presence of ectoenzymes capable offully dephosphorylating ATP. Concerning the effect of P1 activationon RVD, 5 ␮M adenosine, both in the presence and absence of 100␮M S-(4-nitrobenzil)-6-tioinosine (a blocker of adenosine uptake),decreased RVD40 by 37? 44%, whereas 8-phenyl theophylline, a P1antagonist, increased RVD40 by 15%. Overall, results indicate thatATP, UTP, and UDP, acting via P2, are important factors promotingRVD of trout hepatocytes, whereas adenosine binding to P1 inhibitsthis process.